Have been titting about with this thing this weekend:



And have dug a couple of holes- this one in my back garden:



I want to build a retaining wall from concrete blocks, and render it. It will be approx 5 foot high, 25 foot long. The down hill side will be decked, the back side from this shot will be backfilled, and hopefully turned into a flat lawn.

So....

Where's cheapest for concrete blocks?

Any tips for building the wall? My lodger has some knowledge, and naturally I have extensive experience with Lego , so we should be ok.

How many piers / what intervals?

How deep / wide should the footings be?

Any other hints and tips / pointers welcome

Si